Thin-walled hollow casting and method of making the same



April 10, 1962 R. H. OSBRINK 3,028,666

THIN-WALLED HOLLOW CASTING AND METHOD OF MAKING THE SAME 2 Sheets-Sheet 1 Filed Nov. 4. 1959 i E] I 3 RF? yMO/VD H OSBR/NK INVEN TOR ATTORNEYS April 1952 R. H. OSBRINK 3,028,666

THIN-WALLED HOLLOW CASTING AND METHOD OF MAKING THE SAME Filed Nov. 4, 1959 2 Sheets-Sheet 2 (5 35 [5O 5/ A A Z/ 4%:2/ /A RHyMo/vD I1 OSBRl/VK INVENTOR BY M ATTORNEYS United States Patent Ofilice 3,028,666 Patented Apr. 10, 1962 partnership Filed Nov. 4, 1959, Ser. No. 850,972 3 Claims. (Cl. 29-527) My invention has to do with method of and means for producing hollow, thin-walled castings, principally castings of non-ferrous metals, and is a continuation in part of my application No. 453,027 filed August 30, 1954, now abandoned.

In the making of hollow, thin-walled precision metal castings, it is, of course, necessary to use core supports for supporting the core sand as well as to vent gases from the mold. This leaves holes in the casting which must be refilled, and the problem of filling those holes without changing the characteristics of the metal of the casting in the areas around the holes, and without rendering the casting unable to withstand internal and external pressures, and to withstand load pressures in all directions, has heretofore been insurmountable to the extent that many products which could be more advantageously produced by precision casting in sand molds have had to be made by machining.

For instance, prior to my invention it was impossible successfully to cast usable unitary wing sections of airplanes because the only way of filling the core support holes has been by welding. Welding however, changes the characteristics of the metal of the casting in the area around the holes and renders the casting impracticable for use due to the various pressures and stresses which a wing section must be capable of withstanding.

By my invention it is now possible to precision cast in sand molds, complete unitary wing sections of airplanes which sections will withstand all the stresses and internal and external pressures which such sections must be capable of withstanding in use.

It is therefore an object of my invention to provide a novel method of forming thin-walled metal castings which have uniformity of characteristics of the metal throughout the casting and which are capable of withstanding tremendous stresses in all directions as well as internal and external pressures.

it is also an object of my invention to provide a novel method of filling the holes which are left in such a casting after the core supports are removed and after the gases generated in the casting have been vented from the casting.

A further object is to provide a novel, hollow, thinwalled, non-ferrous metal casting having useful characteristics never before attained.

Other objects and corresponding advantages will become apparent hereinafter.

For the purpose of enabling those skilled in the art to make and practice my invention, I shall now describe a presently preferred embodiment thereof for which purpose I shall refer to the accompanying drawing wherein:

FIG. 1 is a plan view of a casting made in accordance with my invention;

FIG. 2 is a sectional view of a mold used in carrying out my invention;

FIG. 3 is a longitudinal sectional view of the casting after the core supports and core sand have been removed;

FIG. 4 is an enlarged section taken on line 44 of FIG. 3; 7

FIGS. 5, 6, 7, 8 and 9, respectively, are enlarged sectional views showing a casting in various stages of completion; and

FIG. 10 is an enlarged side elevational view of a plug device used in my invention.

Referring now to the drawing, I show a finished casting 5 (FIG. 1) in the form of a wing section of an airplane.

In making such a casting in accordance with my invention I first form a sand mold 10 having an outer portion 15 of packed sand carried in a moldbox or flask 17. A sand core 20 is supported from the outer portion 15 by means of a plurality of core supports 22. Each of the core supports has a conoidal head portion 22a which is embedded in the outer sand portion 15, and a cylindrical shank portion 22b extending into the mold cavity into supporting engagement with the core 20.'

For the purpose of venting gases generated in the mold cavity 25 by the casting operation, I form a venting passageway 24 in one or more of the core supports. Said venting passageways also extend through the outer portion 15 of the mold and register with corresponding venting openings, not shown, in the mold box or flask.

It will be observed that the cavity 25 is relatively thin in section-in practice, where an airplane wing section is being cast, the thickness of the section typically would be of a thickness of the order of about .130". However, the cavity includes an annular space 27 of greater thickness or depth around each of the core supports 22 to form an inwardly disposed boss portion, to be described, around each of the openings, to be described. Molten non-ferrous metal, such for instance as magnesium, is then introduced into the mold cavity 25 in the conventional manner through an opening, not shown, to fill the cavity, and, after the metal filling the cavity has hardened, the mold sand 15 and the core supports 22 are removed, leaving the casting at that stage as shown in FIG. 3. The casting, in said condition, has openings 30 surrounded by inwardly extending boss portions 31.

As best shown in FIG. 4, the holes 30, when unfinished, are roughly cylindrical before being machined smooth as shown in FIG. 5. The holes 36, as shown in FIG. 4, are machined into truly cylindrical shape as shown in FIG. 5, there being machined in the casting at the outer end of the hole a conoidal recess or seat 35. As shown in FIG. 6 I then thread the holes 30 as shown at 36.

Each of the holes '30 is then ready to be closed by means of my threaded plug 49, preferably made of the same metal as the casting, now to be described.

As best shown in FIG. 10, each of the plugs 40 has: a threaded shank portion 40a, whose threads mate with threads 36 in the holes St a conoidal head 4012 having an integrally formed twist-oif neck 40c, and an octagonal or angular tool receiving portion 40d for the reception of an installing tool such as a wrench, not shown.

It is my preference to so form the conoidal recess or seat .35 and the conoidal head 40!), that the angle of the head 49b to the longitudinal axis of the plug is approximately 2 greater than is the angle of the seat 35 to said aXlS.

it is also my preference to cool the plug before threading it into the hole as by refrigerating it by ice to shrink the plug. Then, while the plug is still in cooled or shrunken condition, I use a suitable tool such as a Wrench to thread the plug into the hole 36 until the conoidal head 46b is flexed by reason of the material thereof being inherently flexible, into peripheral frictional engagement with the seat 36, and until the twist-off neck portions 400 are severed, after which the casting and plugs are allowed to resume their normal room temperature, which of course results in the plugs expanding into tighter en gagement in the holes.

The head of the plug, and the remaining fragment of the twist-off stem or neck, are then machined off so that the outer end of the plug is truly flush with the outer surface of the casting in the areas of the holes.

By the use of my method the holes which remained in the casting after removal of the core supports and core sand, are closed by my plugs, mounted in tight sealing engagement with the casting and flush with the outer surface of the casting, without in any way altering the characteristics of the metal of the casting in the areas surrounding the plugs. In other words, the plugs in effect become integrated with the casting so that the casting is capable of withstanding stresses in all directions and is capable of withstanding both internal and external pressures, to the same extent as if the plugs had been cast as integral parts of the casting. The relatively different angles of the head 40b of the plugs and the seats 35 result in the plug being retained in tension to prevent the threads of the plugs from working loose in the holes, which result is enhanced by the expansion fit oi the plugs in the holes.

I claim:

1. In the metal molding art, the method of making hollow thin-walled castings which comprises the steps of providing a sand mold, a sand core for said mold having spaced recesses in its opposite surfaces, supporting said core in cavity-defining relationship to said mold by anchoring one end of each of said supports in said mold and engaging the other end thereof in said respective recesses, forming in said cavity a casting having inwardly disposed boss portions surrounding said respective core supports While venting gases from said cavity through said core supports from said cavity thereby leaving holes in said casting for removal of said sand core, removing said sand core through said holes, threading each of said holes, forming a conoidal seat in the casting at the outer end of each of said holes, providing a plurality of threaded plugs for said respective holes each having a conoidal head portion, threading said respective plugs into said respective holes until the said conoidal heads thereof are in sealing engagement with said respective seats, and

machining the head portions of said respective plugs flush with the surrounding surface of said casting.

2. The method of claim 1 wherein the head portion of each of said plugs is provided with a twist-off portion, and which additionally includes the step of severing said twist-off portions from said plugs when the head portions of said plugs are in sealing engagement with said respective seats.

3. In the metal casting art, the method of making a hollow, thin-walled casting in a sand mold which includes the steps of forming a hollow thin-walled casting having an inwardly disposed boss portion presenting an axial hole therethrough and the wall of the casting, threading said hole, forming a conoidal seat in said casting around the outer end of said hole, providing a threaded plug for said opening having a conoidal head portion whose conoidal surface is disposed at a greater angle to the longitudinal axis of said hole than is the angle of said seat, threading said plug into said opening until said head portion of said plug is flexed into position parallel with and in sealing engagement with said seat, and machining the outer end surface of said head portion flush with the surrounding surface portion of the wall of the casting.

References Cited in the file of this patent UNITED STATES PATENTS 1,336,224 Hancock Apr. 6, 1920 1,906,953 Enghauser May 2, 1933 2,068,432 Peters Ian. 19, 1937 2,167,609 Dolle July 25, 1939 2,749,609 Francis June 12, 1956 OTHER REFERENCES The Empty and Load Freight Car Brake Equipment, Instruction Pamphlet No. 5047, January 1921, Westinghouse Air Brake Co., Pittsburgh, Pa. (pages 24 and 25, FIGS. 13 and 14 relied on). 

